Structure of the Maturing 90S Pre-ribosome in Association with the RNA Exosome.

Ribosome assembly is catalyzed by numerous trans-acting factors and coupled with irreversible pre-rRNA processing, driving the pathway toward mature ribosomal subunits. One decisive step early in this progression is removal of the 5' external transcribed spacer (5'-ETS), an RNA extension at the 18S rRNA that is integrated into the huge ...
90S pre-ribosome structure. Upon endo-nucleolytic cleavage at an internal site, A1, the 5'-ETS is separated from the 18S rRNA and degraded. Here we present biochemical and cryo-electron microscopy analyses that depict the RNA exosome, a major 3'-5' exoribonuclease complex, in a super-complex with the 90S pre-ribosome. The exosome is docked to the 90S through its co-factor Mtr4 helicase, a processive RNA duplex-dismantling helicase, which strategically positions the exosome at the base of 5'-ETS helices H9-H9', which are dislodged in our 90S-exosome structures. These findings suggest a direct role of the exosome in structural remodeling of the 90S pre-ribosome to drive eukaryotic ribosome synthesis.
Mesh Terms:
Binding Sites, Cryoelectron Microscopy, DEAD-box RNA Helicases, Endoribonucleases, Exonucleases, Exosome Multienzyme Ribonuclease Complex, Models, Molecular, Protein Binding, Protein Biosynthesis, Protein Conformation, alpha-Helical, Protein Conformation, beta-Strand, Protein Interaction Domains and Motifs, RNA Stability, RNA, Ribosomal, 18S, Ribosomes, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins
Mol Cell
Date: Dec. 21, 2020
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